1. Field of the Invention
The present invention relates to a document sheet feeder and more particularly to a document sheet feeder used with a copying machine, a facsimile or the like so as to feed sequentially document sheets set on a document sheet stacker one for each time to a predetermined position.
2. Description of the Prior Art
In general a document sheet feeder which is used with a copying machine, a facsimile or the like must separate one sheet for each time from a stack of sheets set on a document sheet stacker in a positive manner and feed the sheet thus separated to a predetermined position within a short period of time.
Furthermore, document sheet feeders are generally used in office rooms or the like so that they are required not to produce noise.
Conventionally, various types of document sheet feeders of the type described above have been disclosed and demonstrated. For instance, Japanese Utility Model Publication No. 62-44611 (1987) discloses a document sheet feeder of the type in which a separation pawl having a tapered portion for abutting to the leading edge of a sheet is arranged in opposing relationship to a separation roller. A flexible brake plate made of rubber is disposed behind the separation pawl so that a lowermost sheet of a stack of sheets is separated and fed.
In another document sheet feeder, elastic members in the form of a semi-cylinder are attached at opposite ends of rod-shaped member so that upon rotation of the latter about the center of the member, the semi-cylindrical elastic members separate an uppermost sheet from a stack of sheets and feed it to a predetermined position.
Furthermore, in general, in order to maintain the separated sheet fed to a predetermined position for the sake of the post processing, a one way clutch or the like is used to interrupt the feed of the sheet in conventional sheet feeders.
However, in the first mentioned conventional sheet feeder, the separation roller made of rubber is used so that noise produced is negligible, but the brake plate is so designed and constructed as to contact with the sheets which have not been fed yet so that there arises problems that each sheet cannot be positively separated from the remainings and consequently a plurality of sheets are separated and fed at one time.
In the case of the second-mentioned conventional document sheet feeder, the semi-cylindrical elastic members are made into contact with one surface of a sheet so that the sheet is fed by frictional forces of the semi-cylindrical elastic members. As a result, the separation of each sheet from a stack of sheets can be relatively satisfactorily carried out, but there is a problem that high-level noise is produced when the semi-cylindrical elastic members contact with the surface of the sheet.
Furthermore, in the conventional sheet feeder which uses a one way clutch to interrupt a feed of a sheet, there arises problems that those mechanisms are complicated so as to be expensive, and it is not easy to remove jammed sheets.